1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, to patient ventilation devices, such as breathing circuits and tracheal tubes.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such characteristics of a patient. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine.
Physiological characteristics that physicians may desire to monitor include constituents of the blood and tissue, such as oxygen and carbon dioxide. For example, abnormal levels of carbon dioxide in the blood or tissue may be related to poor perfusion. Thus, assessment of carbon dioxide levels may be useful for diagnosing a variety of clinical states related to poor perfusion. Carbon dioxide and other blood constituents may be directly measured by taking a blood sample, or may be indirectly measured by assessing the concentration of those constituents in the tissue or respiratory gases. For example, carbon dioxide in the bloodstream equilibrates rapidly with carbon dioxide in the lungs, and the partial pressure of the carbon dioxide in the lungs approaches the amount in the blood during each breath. Accordingly, physicians often monitor respiratory gases during breathing in order to estimate the carbon dioxide levels in the blood.
In the course of treating a patient, a tube or other medical device may be used to control the flow of air, food, fluids, or other substances into the patient. For example, medical devices, such as tracheal tubes, may be used to control the flow of one or more substances into or out of a patient. Such tracheal tubes may include endotracheal (ET) tubes or tracheostomy tubes. In this way, substances can only flow through the passage via the tube or other medical device, allowing a medical practitioner to maintain control over the type and amount of substances flowing into and out of the patient. Such airway devices may be part of a breathing circuit that allows a physician to facilitate mechanical ventilation of the patient.
In certain instances, it may be advantageous to assess carbon dioxide in respiratory gases that are flowing through airway devices. The carbon dioxide levels in such gases are generally less contaminated by environmental gases because the airway devices provide at least a partial barrier to the egress or ingress of gas. Further, such information is useful to a healthcare practitioner to determine whether the airway device is transferring sufficient respiratory gas to the lungs or to determine whether the patient is metabolizing the respiratory gas and producing the expected levels of carbon dioxide or other volatile metabolites. Thus, sampling carbon dioxide in an airway device may provide a useful method of assessing physiological carbon dioxide levels.